The drainage of cerebrospinal fluid to alleviate hydrocephalus is now an accepted and highly developed art. Early devices for this purpose were little more than a drainage tube with a unidirectional check valve which was often formed as a slit in the wall. These have now been superseded by systems which allow for a pumping action to withdraw fluid from a region, for flushing action to clear obstructions from the system, for routine flow at established differential pressures, and for minimizing excess drainage that can occur when the patient abruptly changes his position.
Excess drainage most frequently occurs when, after the patient has laid down for a time, he sits or stands up. Then the full system, which was nearly horizontal with only a small differential in elevation between the body regions, becomes nearly vertical with a tall column of fluid tending to flow out of the downstream end. This exerts a substantial suction in the system that can result in over-drainage.
As examples of the prior art, Schulte Pat. No. 3,111,125 shows a pumping device that is palpable from outside which enables the system to be flushed downstream of the pump, and for fluid to be pumped from upstream. Schulte Pat. No. 3,769,982 shows a system which has closure means responsive to downstream suction, in which an anti-siphon valve closes when downstream suction exceeds some predetermined level. These are commercially accepted systems, but they still suffer from some disadvantages which it is the purpose of this invention to overcome.
A variability of control, especially to prevent excessive drainage, is a desirable objective in systems of this type. It should be remembered that cerebrospinal fluid is being withdrawn from within and around the brain, and that either excessive pressure in, or excessive drainage of fluid from the cranium, are consequences to be avoided. Insufficient drainage results in the classical consequences of hydrocephalus--excessive pressure and possible brain damage. Excessive drainage results in acute discomfort with headaches, lassitude and mental obtundity or may chronically lead to the slit ventricle syndrome.
A valve which responds to an unfavorable circumstance such as suction with merely an off or on choice may be better than no control at all, but a compensating valve which can respond proportionally (even though closure may be one of the potential settings) is much to be preferred. A simplistic off/on choice is likely to confine the operation of the system to only certain circumstances, whereas it is much better if the drainage can be continuously controlled. This invention provides an improved differential pressure valve which not only responds to upstream and downstream pressure, but also to a third "reference" external force or pressure. It can be used for pumping and flushing, and as a compensating valve that can provide proportional settings between the three control pressures rather than merely off and on settings.
While cerebrospinal fluid drainage from the brain is disclosed herein as the best known use for this device, it is evident that the device is also useful to drain other fluid from other body regions. The invention is not to be limited to the disclosed use.